#include <glad/glad.h>
#include <GLFW/glfw3.h>

#include <iostream>

void framebuffer_size_callback(GLFWwindow* window, int width, int height);
void processInput(GLFWwindow *window);

// settings
const unsigned int SCR_WIDTH = 800;
const unsigned int SCR_HEIGHT = 600;

int main()
{
    // glfw: initialize and configure
    // ------------------------------
    glfwInit();
    glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR, 3);//主版本号
    glfwWindowHint(GLFW_CONTEXT_VERSION_MINOR, 3);//次版本号
    glfwWindowHint(GLFW_OPENGL_PROFILE, GLFW_OPENGL_CORE_PROFILE); //核心模式

#ifdef __APPLE__ //苹果电脑
    glfwWindowHint(GLFW_OPENGL_FORWARD_COMPAT, GL_TRUE);
#endif

    // glfw window creation
    // --------------------
    GLFWwindow* window = glfwCreateWindow(SCR_WIDTH, SCR_HEIGHT, "学习OpenGL", NULL, NULL);
    if (window == NULL)
    {
        std::cout << "Failed to create GLFW window" << std::endl;
        glfwTerminate(); //终止
        return -1;
    }
    glfwMakeContextCurrent(window); //上下文
    glfwSetFramebufferSizeCallback(window, framebuffer_size_callback); //回调函数

    // glad: load all OpenGL function pointers
    // ---------------------------------------
    if (!gladLoadGLLoader((GLADloadproc)glfwGetProcAddress)) //加载函数指针
    {
        std::cout << "Failed to initialize GLAD" << std::endl; //初始化失败
        return -1;
    }    

    // render loop
    // -----------
    while (!glfwWindowShouldClose(window)) //循环渲染
    {
        // input
        // -----
        processInput(window); //输入

        // render
        // ------
        glClearColor(0.2f, 0.3f, 0.3f, 1.0f); //清屏
        glClear(GL_COLOR_BUFFER_BIT); //清屏

        // glfw: swap buffers and poll IO events (keys pressed/released, mouse moved etc.)
        // -------------------------------------------------------------------------------
        glfwSwapBuffers(window); //交换缓冲
        glfwPollEvents(); //轮询事件
    }

    // glfw: terminate, clearing all previously allocated GLFW resources.
    // ------------------------------------------------------------------
    glfwTerminate(); //终止
    return 0;
}

// process all input: query GLFW whether relevant keys are pressed/released this frame and react accordingly
// ---------------------------------------------------------------------------------------------------------
void processInput(GLFWwindow *window)
{
    if(glfwGetKey(window, GLFW_KEY_ESCAPE) == GLFW_PRESS) //按下esc
        glfwSetWindowShouldClose(window, true); //关闭窗口
}

// glfw: whenever the window size changed (by OS or user resize) this callback function executes
// ---------------------------------------------------------------------------------------------
void framebuffer_size_callback(GLFWwindow* window, int width, int height)
{
    // make sure the viewport matches the new window dimensions; note that width and 
    // height will be significantly larger than specified on retina displays.
    glViewport(0, 0, width, height); //视口
}